The Synopsis on the Alatriste Film Site

In Imperial Spain of the 17th century, Diego Alatriste, a courageous soldier in his Majesty's service, fights in a war in the cold lands of Flanders. In an ambush by the Dutch, Balboa, his friend and comrade in arms, is mortally wounded. Alatriste listens to a last request from the lips of his friend and promises to fulfill it: he will care for his son Inigo and keep him away from a career as a soldier.

On his return to Madrid, Alatriste finds a dying empire. The same Spain in which Quevedo and Gongora write their verses, Velazquez paints his paintings, and Lope de Vega gets his plays performed, is collapsing under the impassivity of its King. The court of Philip the IV, dominated by intrigues and corruption, is handled by Count-Duke of Olivares as he pleases, with the support of the Holy Inquisition.

Alatriste himself, who ekes out a living by hiring his sword, will be involved in one of these intrigues when he is hired, together with another mercenary, the Italian Gualterio Malatesta, to kill two mysterious persons who are traveling incognito to Madrid. The future of Alatriste will be marked when, suspecting there is something shady about this sinister job, he decides to spare the life of the two foreigners and confronts Malatesta who wanted to finish the job. That night he will win an enemy for all of his life.

When Alatriste discovers whose lives he has saved, he understands that he will have to confront forces too powerful to fight with the sword.

But he will not be alone, his inseparable comrades on the battlefield, the extremely beautiful Maria de Castro and above all, Inigo, now almost a son to him, will be the unconditional support of the Captain and key characters in this grand adventure story.